We have conducted experiments using Octopus vulgaris as an experimental animal that have given some new insights into the nature of the processes that take place in a learning neuropil during the learning process that might be applicable to the human brain. In particular we have studied a neuropil in which we know that tactile learning is taking place during a training period and have found two related things that suggest experiments that we propose to do with human brain material that may relate to the learning and memory deficiencies of Alzheimer disease. We have postulated that a primary step in learning is rearrangements of neurites in the participating neuropils that is a preamble to the formation of new synapses. If this is so then one would expect to see some signs of growth cone activity and one of the most prominent of these is the extension of filopodia. It follows that injection into the neuropil of cytochalasin B should block learning because this drug leads to depolymerization of actin which must be polymerized for filopodial extension. Further the drug should not affect existing memories. Our experiments show that both these conditions are met in Octopus, supporting our general hypothesis. We have also conducted a preliminary morphometric study of the same neuropil during training and found that as the animal begins to learn there is an increase in the volume frequency of filopodia. On the basis of these findings it is reasonable to ask whether or not there is evidence in human brain neuropils of filopodial activity that may be involved in learning and memory. We therefore plan to study human brain material by electron microscopy to answer this question. In particular we plan to collect specimens containing neuropils from regions of the human brain that might be involved in learning and study them by electron microscopy looking specifically for filopodia. We shall concentrate on the hippocampus but shall take specimens from frontal, parietal, temporal and occipital lobe cortex. We shall study them by transmission and scanning electron microscopy techniques. Our aim is to determine whether or not the brains of Alzheimer disease patients differ than normal brains in regard to the above structural features and in any case to describe the Alzheimer's and normal brains with respect to these features.